Various microbicidal and microbiostatic compositions are known for use in a variety of prophylactic applications. These compositions, however, suffer from disadvantages in that the compositions may be active toward only a narrow range of microbes or have low activity, requiring inordinate amounts for useful effects. Some of the known compositions produce undesirable side effects or have such degrees of toxicity that the use thereof is not practical. For example, while ordinary soap (salts of long chain aliphatic acids) is a very mild and well-tolerated prophylatic composition, the activity of soap is restricted to a relatively narrow group of microbes. On the other hand, methanol is effective against a relatively wide range of microbes, but produces considerable discomfort to the animal user when applied to open tissue, sensitive skin or internal membranes. It is also toxic. Hexachlorophene is active against a relatively wide range of microbes and is mild, but it has a possible undesired side effect, i.e., it has been indicated as a carcinogen.
In addition to the foregoing difficulties, special applications of microbicides impose even more stringent requirements. For example, where microbicides may be ingested by animals, e.g., humans, in substantial quantities, they must be non-toxic in ingested amounts. In this latter regard, the LD.sub.50 of a microbicide may be higher when only small amounts would normally be ingested, for example, when used in cleaning eating utensils, in comparison with applications where larger amounts are nomally ingested, for example, when used to sanitize automatic milking equipment.
The most demanding applications in the foregoing regard, are when the microbicide is an ingredient in a composition that may be directly ingested, e.g., lipstick compositions, toothpaste, mouthwash and even in food compositions. This kind of application requires that the microbicide be "food-grade" and it is to this most stringent application that the present invention has particular relevance.